The present invention relates to roadway vehicle detection systems and more particularly to a self-powered vehicle detector coupled by an RF link to a remotely located traffic control device.
Vehicle detectors are key components in all street and freeway traffic control and surveillance systems. An ideal detector for these applications should meet such requirements as low cost, accurate detection, minimum installation time and cost, reliability under all environmental conditions, low maintenannce and calibration requirements, and ability to detect all vehicles on any standard roadway surface.
Prior vehicle detection systems typically include an inductive loop or coil of wire buried in the pavement and coupled to electronic sensing circuits controlled by changes in the loop inductance when a vehicle passes thereover. A hardwired or transmitter/receiver link couples the detector signal to a traffic control device. Inductance loop systems require considerable time and cost for installation and removal, and many self-powered systems have a limited operational life due to a relatively high power consumption. Another vehicle detection problem arises when a vehicle is stopped over a detector for an extended period of time, which could disable prior systems until the vehicle is removed.